Ultra-compact, high-NA achromatic multilevel diffractive lens via metaheuristic approach

TL;DR

This paper presents a novel design of an ultra-compact, high-NA achromatic multilevel diffractive lens operating in microwave frequencies, optimized with a metaheuristic algorithm, and experimentally validated using 3D printing.

Contribution

It introduces a multi-objective differential evolution algorithm for designing achromatic diffractive lenses with adjustable focal distance, enabling phase profile tailoring without preset parameters.

Findings

Achieved a high NA (~0.99) diffraction-limited lens in microwave range.

Demonstrated successful fabrication and experimental validation of the lens.

Scaled the design to visible wavelengths showing achromatic focusing.

Abstract

Recently, the multilevel diffractive lenses (MDLs) have attracted considerable attention mainly due to their superior wave focusing performance; however, efforts to correct the chromatic aberration are still in progress. Here, we demonstrate the numerical design and experimental demonstration of high-numerical aperture (NA) (${\sim}0.99$), diffraction-limited achromatic multilevel diffractive lens (AMDL) operating in microwave range $10 GHz$ - $14 GHz$. A multi-objective differential evolution (MO-DE) algorithm is incorporated with the three-dimensional finite-difference time-domain (3D FDTD) method to optimize both the heights and widths of each concentric ring (zone) of the AMDL structure. In this study, the desired focal distance ${\Delta}F_d$ is treated as an optimization parameter in addition to the structural parameters of the zones for the first time. In other words, MO-DE diminishes the necessity of predetermined focal distance and center wavelength by also providing an alternative method for phase profile tailoring. The proposed AMDL can be considered as an ultra-compact, the radius is $3.7{\lambda_c}$ where ${\lambda_c}$ is the center wavelength (i.e., $12 GHz$ frequency), and flat lens which has a thickness of ${\lambda_c}$. The numerically calculated full-width at half-maximum (FWHM) values are below $0.554{\lambda}$ and focusing efficiency values are varying between $28{\%}$ and $45.5{\%}$. To experimentally demonstrate the functionality of the optimized lens, the AMDL composing of polylactic acid material (PLA) polymer is fabricated via 3D-printing technology. The numerical and experimental results are compared, discussed in detail and a good agreement between them is observed. Moreover, the verified AMDL in microwave regime is scaled down to the visible wavelengths to observe achromatic and diffraction-limited focusing behavior between $380 nm$ - $620 nm$ wavelengths.